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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 23, issue 2
Ann. Geophys., 23, 545–552, 2005
https://doi.org/10.5194/angeo-23-545-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 545–552, 2005
https://doi.org/10.5194/angeo-23-545-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  28 Feb 2005

28 Feb 2005

Shock parameter calculations at weak interplanetary shock waves

J. M. Gloag and A. Balogh J. M. Gloag and A. Balogh
  • Imperial College Space and Atmospheric Group Department of Physics, Prince Consort Road, London SW7 2BW, UK

Abstract. A large set of interplanetary shock waves observed using the Ulysses spacecraft is analysed in order to determine their local parameters. For the first time a detailed analysis is extended to the thermodynamic properties of a large number of events. The intention is to relate the shock parameters to the requirements set by MHD shock theory. A uniform approach is adopted in the selection of up and downstream regions for this analysis and applied to all the shock waves. Initially, the general case of a 3 component adiabatic plasma is considered. However, the calculation of magnetosonic and Alfvénic Mach numbers and the ratio of downstream to upstream entropy produce some unexpected results. In some cases there is no clear increase in entropy across the shock and also the magnetosonic Mach number can be less than 1. It is found that a more discerning use of data along with an empirical value for the polytropic index can raise the distribution of downstream to upstream entropy ratios to a more acceptable level. However, it is also realised that many of these shocks are at the very weakest end of the spectrum and associated phenomena may also contribute to the explanation of these results.

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